1. Field of the Invention
The invention in general relates to flow meters, and more particularly to a method of determining a correction factor for multipath acoustic flow meters.
2. Description of the Prior Art
Various systems exist for measuring volumetric flow rate in a fluid carrying conveyance. For many uses of such systems accuracy is a prime consideration in that an error, for example of 1%, in fluid flow measurement can represent many thousands of dollars. Accurate knowledge of volumetric flow rate is required for situations such as metering water to communities, measuring efficiency of various hydroelectric equipment, sewage treatment plants, and oil pipeline monitoring to name a few.
There are many piping conditions which will cause asymmetric distortions in the axial velocity profile of the flowing fluid. For example, distorted velocity profiles can be expected downstream of bends, tees, valves and other devices which may be within the flow field.
Flow measurement systems utilizing the propagation of acoustic energy through the fluid have demonstrated that volumetric flow, even with distorted velocity distributions can be measured to a relatively high degree of accuracy. One such highly accurate system is based upon time measurements of acoustic pulses propagated in opposite directions across the fluid medium. A plurality of acoustic paths are provided at specified locations and their individual flow readings are combined according to a numerical integration technique such as the Gaussian technique to compute volumetric flow rate. These systems are well known and are described for example in U.S. Pat. Nos. 3,564,912; 3,940,985; 4,024,760 and in application Ser. No. 748,258 filed Dec. 6, 1976, assigned to the present assignee.
For such multipath acoustic systems it would be desirable to establish the possible error, and the bounds on that error for general flow distortions. The present invention provides such method.